Electrophotographic machines, such as laser printers, photocopiers, fax machines, etc., comprise a main assembly and a replaceable supply cartridge. The main assembly includes, inter alia, a housing, a control panel situated on the housing, an electronic control system, a motor, a gear train driven by the motor in response to the operation of the control panel, and electric contacts for delivering power to the supply cartridge inserted into, and retained within, grooves or channels in the opposed side walls of the housing. An optical projection system, which transmits images to the photosensitive drum, is located within the housing, and a central processor controls the sequence and timing of the mechanism operations.
The supply cartridge comprises a shell including, inter alia, a photosensitive drum, a charge roller for charging the photosensitive drum, a toner supply, and a developer roller for developing the latent image on the photosensitive drum. The rotational force imparted to the photosensitive drum is transmitted to each roller within the process cartridge. A latent image is transmitted by the optical projection system, in the machine housing, to the photosensitive drum, via a window or aperture in the cartridge. The storage member, usually paper, is retained in a cassette in the machine housing, and the advance of the paper through the machine is controlled by the gear train.
The electrographic (EP) machine includes a minimum number of moving parts, and is designed to function effectively for extended periods of time. The supply cartridge contains a limited supply of toner, and will be replaced numerous times over the life of the electrophotographic machine. The supply cartridge is configured to be readily removed, and accurately replaced, within the electrophotographic machine, with a minimum of effort, by office personnel.
One end of the photosensitive drum protrudes for connection to the gear train in the electrophotographic machine; the gear train imparts rotational force directly to the photosensitive drum and indirectly to the several associated drums, or rollers, within the supply cartridge.
An aperture is formed in one face of the gear train in the electrophotographic printer to receive the protruding end of the photosensitive drum. After the protruding end, or projection, of the photosensitive drum is properly seated in the gear train, the motor, when energized, supplies sufficient power to drive the gear train, the photosensitive drum, and the associated rollers within the supply cartridge.
An interface is defined between the supply cartridge by the protruding end of the photosensitive drum and the recess in the gear train of the electrophotographic machine. Such interface must be sturdy, and reliably, facilely and accurately established in the field, and provide for slip free power transmission to the cartridge and the several interconnected drums and rollers retained therein for the useful life of the cartridge. The interface must also be modest in cost, for price competition in the area of replacement supply cartridges is severe.
One technique for responding to the foregoing requirements is set forth in U.S. Pat. No. 5,023,660, granted Jun. 11, 1991, to Ebata et al. As shown in FIG. 4 of such patent, the image bearing member (photosensitive drum 1) includes a shaft receiving portion (central bore 2f), adjacent its center, to receive a positioning shaft (4) of the main assembly (of the photocopier), that correctly positions the image bearing member relative to the main assembly. Driving force is transmitted to the photosensitive drum by a drive transmission member (10) with projecting pins (10a) which engage ribs (2d) in the flange (2) formed in the protruding collar (2c) on the drum. The inner end of the metallic shaft contacts conductive plate (13) and establishes an electrical connection with the image bearing member for grounding same; a spring (12) normally urges the drive transmission member toward the photosensitive drum.
Another technique for transmitting driving force to the supply (or process) cartridge for an electrophotographic machine is disclosed in European patent application EP 0735 432 A1, published Oct. 2, 1996. Such technique employs a side gear (34) in the drive train (13) of the electrophotographic machine, such gear having recess (twisted hole 18a) formed in one face. A twisted, prism shaped projection (17a) extends outwardly from one end of the photosensitive drum within the supply (or process) cartridge (as shown in FIGS. 10 and 11). When the side gear is longitudinally advanced toward the twisted, prism-shaped projection, the projection enters the recess to establish a connection therebetween (as shown in FIGS. 13 and 14). The advancement of the side gear may be linked to the opening of cover (14) for the electrophotographic machine (note rod 37 in FIGS. 15-17).
Whereas the drive transmitting mechanisms described above functioned satisfactorily, certain shortcomings were noted. For example, the drive transmitting system described by Ebata et al requires a coil spring to maintain a constant biasing force upon the drive transmission element; such consistency is not easily maintained over extended periods of operation.
The European published patent application relies upon a twisted projection and a twisted hole for receiving same; the twisted projection is difficult and costly to mold within tight dimensional tolerances, and to remove same from a mold without injuring same.